This invention relates to the preparation of metallopolysilanes. More specifically this invention relates to the preparation of metallopolysilanes which contain significant amounts of aluminum, boron, chromium, lanthanum, molybdenum, neodymium, niobium, samarium, tantalum, titanium, tungsten, vanadium, yttrium, or zirconium. Such metallopolysilanes can be prepared with relatively low oxygen contents. These polymers are useful as chemical intermediates to synthesize other metal-containing organosilicon materials or polymers. These polymers can also be converted, when fired at high temperatures, to ceramic materials. Ceramic materials can be produced which are low in oxygen.
What is disclosed herein is a novel process to obtain novel metallopolysilanes which consists of contacting and reacting organohalogendisilanes with metal-containing compounds in the presence of a redistribution catalyst in an inert, essentially anhydrous atmosphere and removing volatile byproducts.
Haluska in U.S. Pat. No. 4,482,689 (issued Nov. 13, 1984) described a method of preparing metallosilazane polymers containing boron, phosphorous, or titanium by reacting chlorine-containing disilanes with disilazanes and a reactive metal halide without any added catalyst. When the Haluska reaction mixture was heated in an inert, essentially anhydrous atmosphere the following reactions, where ##STR1## is the reactive metal halide, were thought to take place: ##STR2## where M' is boron, phosphorous, or titanium, X is halogen, and R* is an alkyl radical containing 1 to 3 carbon atoms, a vinyl radical, or a phenyl radical. Based on this reaction scheme, the incorporation of the metal into the polysilazane occurs only through the silazane moiety. In other words, Haluska teaches that there is no direct interaction between the chlorine in the disilanes and the metal halides.
Yajima et al. in U.S. Pat. No. 4,220,600 (issued Sept. 2, 1980) disclosed a method for preparing a polycarbosilane by reacting a polyborosiloxane with a polysilane. The polyborosiloxanes were prepared by reacting boric acid (or its ester) with a diorganodichlorosilane or by reacting boric acid with diorganodialkoxylsilane. The preparation of borosiloxane polymers from boric acid and phenylsilane is described by Yajima et al. in U.S. Pat. No. 4,152,509 (issued May 1, 1979). The required polysilanes were prepared by dechlorinating a dichlorosilane with sodium metal. Therefore the method of Yajima required at least three reaction steps to prepare a polycarbosilane. The polycarbosilane contained significant amounts of oxygen in the polymer chain in the form of siloxane or B-O bonds. The polycarbosilane formed a ceramic material upon firing at high temperature. The ceramic yield was higher for the boron-containing polycarbosilane relative to a similar polycarbosilane without boron.
In U.S. Pat. No. 4,359,559 (issued Nov. 16, 1982), Yajima et al. repeated the preparation of a polymetallocarbosilane by reacting a polycarbosilane containing ##STR3## units with metal-containing compounds of the formula M"B.sub.4 where R.sup.1 was a hydrogen atom, lower alkyl radical, or a phenyl radical and M" was either titanium or zirconium and B was an alkoxy group, a phenoxy group, or an acetylacetoxy group. The polymetallocarbosilane produced by this method contains significant amounts of oxygen in the polymer chain in the form of M"-O bonds. A ceramic material was formed upon firing the polymetallocarbosilane at elevated temperatures.
In U.S. Pat. No. 4,347,347 (issued Aug. 31, 1982), Yajima et al. disclosed an organometallic copolymer containing a polycarbosilane portion and a polymetallosiloxane portion which were crosslinked. This copolymer was prepared by reacting a polycarbosilane with a polymetallosiloxane which contained units of formula --[M"--O]-- where M" is either titanium or zirconium and siloxane units of formula --[Si--O]--. This process consists of at least three steps since neither the polycarbosilane or polymetallosiloxane are readily available. The copolymer produced contains significant amounts of oxygen in the polymer chain in the form of siloxane units and --[M"--]-- units. Upon firing at elevated temperatures the copolymer is converted to a ceramic material.
In European Patent Application No. 0048957 (published July 4, 1982) Yajima prepared ceramic fibers from vanadium-modified polycarbosilanes which contained significant amounts of oxygen. The vanadium-modified polycarbosilanes were prepared by reacting polysilanes with either a polyvanadiosiloxane or a vanadium complex containing oxygen at temperatures between 250.degree. and 500.degree. C..
In Japanese Kokai Tokoyo Koho No. 58/213023 and No. 59/161430 titanium- or zirconium-containing preceramic polymers were prepared by reacting polysilanes with titanium alkoxides or zirconium alkoxides. Such materials are expected to contain significant oxygen levels in the form of --[Ti--O]-- or --[Zr--O]-- units.
What has been newly discovered is that certain metallopolysilanes containing only limited oxygen can be prepared by reacting disilanes with certain reactive metal-containing compounds.